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88 Clear or 91 Octane?

Magus2727

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Not sure if this counts for Sports Tuning. The 3.5L EcoBoost and the ECU on the Explorer appears to have an intelligent fuel mapping system that will advance timing and up your HP & TQ figures by advancing the timing if good gas and higher octane is used.

I live in Utah where I am at 4,200 feet. So the best I can get is 91 octane from the pump. A local brand also is offering 88 Clear which is an Ethanol free fuel at 88 Octane.

The 91 Octane can have as much as 15% ethanol in it.

So question is, Which should I be running (price is the same). Should I run a 91 Octane that has some unknown % blend of Ethanol up to 15% or should I run a 88 Octane with no Ethanol.

Thanks.
 


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drudis

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Think of it this way.
Alcohol has 50% BTU (energy) of gasoline, so you use 2x as much.
Given 15% ethanol, thats like 7-1/2% less (half of 15) less energy in a gallon. So you will only be getting 92.5 "units" of energy in a gallon (unlike 100 "units" of energy in a gallon of 88octane).

BUT... the car makes more power (and better fuel economy) tuned to 91 octane.

Therefore its a close call, but personally, I would run the 91.
 




Magus2727

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I wish there was a place that made 91 octane ethanol free, that would be the best.

I know vehicles have gotten a lot better with the ethanol also. they are using gaskets and such that don't brake down with a 15% blend.

I am likely asking a question that has already been asked but what has been the measured fuel economy delta from regular to premium? What I have found was mostly from tuner web sites that are more showing deltas in power when at the +2 mode vs 0 mode of the ECU advancing. With them being the same price I will continue to use the 91 octane, just was not sure if there would be better performance with that 7-1/5% more energy or 3 point higher octane.

I am only at 1,500 miles on my 2018 so am still breaking it in and getting valves and rings seated (well I guess that really is done in the first 200-500 miles). Which being this is the first brand new vehicle I have owned, should I do an oil change in the first bit before going on the 5000-10000 mile oil change schedule?
 




peterk9

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I wish there was a place that made 91 octane ethanol free, that would be the best.

I know vehicles have gotten a lot better with the ethanol also. they are using gaskets and such that don't brake down with a 15% blend.

I am likely asking a question that has already been asked but what has been the measured fuel economy delta from regular to premium? What I have found was mostly from tuner web sites that are more showing deltas in power when at the +2 mode vs 0 mode of the ECU advancing. With them being the same price I will continue to use the 91 octane, just was not sure if there would be better performance with that 7-1/5% more energy or 3 point higher octane.

I am only at 1,500 miles on my 2018 so am still breaking it in and getting valves and rings seated (well I guess that really is done in the first 200-500 miles). Which being this is the first brand new vehicle I have owned, should I do an oil change in the first bit before going on the 5000-10000 mile oil change schedule?
I ran 87 and 89 in my Ecoboost and lately have been using 91. There is a slight increase in MPG with 91 but it definitely is not offset by the increased cost. Looking at it from a dollar and cents perspective 87 gives the best return for the cost. Lots of reading on oil changes here; Oil Change interval
I believe Shell's top grade is ethanol free as a few posts have mentioned.

Peter
 




Magus2727

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Thanks, I just started reading that thread while I was looking around at other things. I will look at the shell. I might have to get there CC option and get the extra per cent discount. The Shells are far and few between here. More Chevrons.

Its about 30 cents more here for the 91 vs the 85 octane (due to altitude the 85 octane is the "regular" grade). so would need to do the math to see what the increase in MPG would have to be to justify the cost. likely would need to be at least a 2-3 MPG increase ( think I am getting about 2.3 MPG increase) so I would have to go from say 19 to 21.3 to break even.
 




Drive XR7

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Marathon in this area is ethanol free 93 octane.
 




Magus2727

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Due to my elevation the highest we get pump gas is 91 octane. Good to know there are places that offer ethonal free on the premium grade.

I need to look into the Shell around here.
 




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